1. Field of the Invention
The present invention relates to an on-vehicle engine control apparatus in which an intake amount of vehicle engine and so on are electronically controlled by an electric motor.
In particular, the invention relates to an on-vehicle engine control apparatus for carrying out electronic control of an intake amount and so on employing a system in which a CPU (microprocessor) is used to carry out main control of ignition/fuel supply of engine and so on as a whole, and by which safety in controlling the whole engine is improved.
2. Description of the Related Art
Electronic throttle control has been widely put into practical use so that intake throttle valve opening of an engine is controlled by an electric motor according to degree of working an accelerator pedal. It is a recent trend to employ a wireless type control without accelerator wire. But there is another type of control that uses an accelerator acting as backup means in combination with a motor, or a further type in which an accelerator wire is used in normal driving and an electric motor is used in constant-speed driving.
On the other hand, the entire engine control includes main control for an engine drive unit such as ignition coil (in case of gasoline engine) or fuel injection valve and auxiliary control for peripheral machine such as a transmission solenoid valve or an air conditioner driving electromagnetic clutch. Various types of CPU have been heretofore proposed in the aspect of combining the engine control with the mentioned throttle control.
FIG. 10 shows a constitution of a CPU for use in an on-vehicle engine control apparatus according to a first type of prior art and, in this type, one single CPU 1a carries out the entire control.
Connected to this CPU 1a are a sensor for detecting an engine speed, a crank angle sensor, an airflow sensor for measuring an intake amount, an intake pressure sensor, an exhaust gas sensor, a coolant temperature sensor, an accelerator position sensor (hereinafter referred to as APS) for measuring a degree of working the accelerator pedal, a throttle position sensor (hereinafter referred to as TPS) for measuring a throttle valve opening, a shift position sensor for detecting a transmission lever position, and a large number of on-off or analog input signals 11a. 
Control outputs of the CPU 1a includes main machinery/auxiliary machinery control outputs 21a such as an ignition coil, a fuel injection solenoid valve, a transmission solenoid valve, an exhaust gas circulation control solenoid valve, etc., and a throttle control motor 22a. 
The Japanese Patent Publication (unexamined) No. 176141/1990 titled xe2x80x9cControl Apparatus for Internal Combustion Enginexe2x80x9d and the Japanese Patent Publication (unexamined) No. 141389/1999 titled xe2x80x9cThrottle Control Apparatus of Internal Combustion Enginexe2x80x9d disclose this first type of prior art as described above in which the entire control is carried out by one single CPU.
A problem exists in such a type of carrying out the entire control using one CPU. For example, such a type of control system is insufficient in safety at the time of occurrence of any error or abnormality in the system, and performance and specification are not sufficiently secured because of a heavy burden on the CPU.
Particularly since it is possible to prevent the engine from running out of control by accurately suppressing an intake amount, control of the intake amount is the most important requirement in terms of safety. Therefore it is a market trend to employ required sensors and CPU in the form of dual system for the electronic throttle control.
FIG. 11 shows a constitution of a CPU for use in an on-vehicle engine control apparatus according to a second type of prior art. In this second type, main machinery and auxiliary machinery 21b are controlled by a first CPU (CPU 1) 1b, and main machinery/auxiliary machinery control input signals 11b is connected to the required CPU.
A second CPU (CPU 2) 2b receives a throttle control input signal 12b of the APS, the TPS, etc. and controls a throttle control motor 22b. A third CPU (CPU 3) 3b receives a monitor control input signal 13b and generates a monitor control output 23b, thereby safety of the electronic throttle control is improved.
The Japanese Patent Publication (unexamined) No. 278502/1994 titled xe2x80x9cCruise Control Apparatusxe2x80x9d and the Japanese Patent Publication (unexamined) No. 2152/1999 titled xe2x80x9cConstant-Speed Driving Apparatus for Vehiclexe2x80x9d do not mention the foregoing first CPU (CPU 1) 1b. But those patent literatures gives a description defined to a throttle control in which the second CPU (CPU 2) 2b acts as a main CPU and the third CPU (CPU 3) 3b acts as a sub-CPU.
In this concept, a constant-speed control apparatus is added to the conventional accelerator-wire-type engine control apparatus, and consequently, the constitution with the three CPUs is complicated and expensive.
FIG. 12 shows a constitution of a CPU for use on-vehicle engine control apparatus according to a third type of prior art. In this third type, main machinery and auxiliary machinery 21c are controlled by a first CPU (CPU 1) 1c. A related main machinery/auxiliary machinery control input signal 11c is connected to the CPU 1c. 
A second CPU (CPU 1) 2c receives a throttle control input signal and a monitor control input signal 12c of the APS, the TPS, and so on, and generates a control output and a monitor control output 22c to the throttle control motor. The first CPU (CPU 1) 1c and the second CPU (CPU 2) 2c monitor each other.
In the CPU constitution of this type, the first CPU (CPU 1) 1c acts as a so-called ECU (engine control unit) and the second CPU (CPU 2) 2c acts as a so-called a TCU (a throttle control unit). In this manner, this constitution intends to improve safety of the entire system through mutual monitoring.
xe2x80x9cEngine Control Apparatusxe2x80x9d disclosed in the Japanese Patent Publication (unexamined) No. 270488/1996 is of a two-CPU constitution in which an accelerator wire is jointly used, and xe2x80x9cThrottle Valve Control Apparatusxe2x80x9d disclosed in the Japanese Patent Publication (unexamined) No. 97087/2000 is of a wireless two-CPU constitution.
Both of them disclose fail-safe control means that enables smooth limp/home driving in case of occurrence of any abnormality.
On the other hand, in the Japanese Patent Publication (unexamined) No. 249015/1994 titled xe2x80x9cControl Apparatus for Vehiclexe2x80x9d, the control apparatus is provided with a bypass valve for limp driving. A motor controls opening of the main throttle valve to be fully closed and returned by a return spring. This prior art discloses limp driving means acting in case of an excess-open abnormality when it is impossible to fully close and return the main throttle valve due to an abnormality in the motor, an actuator, or the like.
In the prior arts described above, an idle cylinder level is set conforming to an output voltage of the throttle position sensor (TPS) that detects a main throttle valve opening and to an output voltage of the accelerator position sensor (APS) that detects a degree of acting the accelerator pedal. Fuel supply to a part of a multi-cylinder engine is stopped, and number of effective cylinders is reduced in order to suppress the engine speed.
In the prior arts as described above, there still remain several problems in using only one single CPU. For example, safety is not assured and a burden on the CPU control is excessively heavy, and it is therefore essential to reduce the burden on the CPU and improve safety monitoring.
However, the engine drive control such as ignition control or fuel injection control is closely related to the throttle control, and it will not be a good idea to carry out separately the engine drive control and the throttle control with separate CPUs.
Accordingly, a first object of the present invention is to provide an on-vehicle engine control apparatus suitable for carrying out an engine drive control and a throttle control together in a batch using one single microprocessor thereby improving safety of the apparatus.
A second object of the invention is to provide fail-safe control means for facilitating limp driving in case of occurrence of any abnormality.
An on-vehicle engine control apparatus according to the invention includes: a motor for carrying out an intake throttle valve opening control conforming to an output of one of a pair of accelerator position sensors that detects a degree of working an accelerator pedal and an output of one of a pair of throttle position sensors that detects the mentioned throttle valve opening; and an engine drive that includes at least one fuel injection solenoid valve.
The on-vehicle engine control apparatus also includes: a load relay that feeds the mentioned motor with a power supply and returns the mentioned throttle valve opening to a predetermined position by interrupting the mentioned power supply; a first integrated circuit element that includes a microprocessor and generates a first control output for controlling a throttle valve to the mentioned motor and a second control output to the mentioned engine drive; and a second integrated circuit element that is connected to the mentioned first integrated circuit element via a serial interface and generates a driving output to the mentioned load relay in cooperation with the mentioned microprocessor of the mentioned first integrated circuit element.
Furthermore, the mentioned on-vehicle engine control apparatus includes: first mutual diagnostic means that is incorporated in the mentioned first integrated circuit element and diagnoses whether or not there is any abnormality in operation of the mentioned second integrated circuit element; second mutual diagnostic means that is incorporated in the mentioned second integrated circuit element and diagnoses whether or not there is any abnormality in operation of the mentioned first integrated circuit element; and abnormality detection means that monitors operation of a sensor system, a control system, and an actuator system related to the mentioned throttle valve control at all times and generates an abnormality detection output at the time of occurring any abnormality.
In the mentioned on-vehicle engine control apparatus, operation of the mentioned load relay is preferably controlled conforming to a diagnostic result of the operation of the mentioned second integrated circuit element carried out by the mentioned first mutual diagnostic means, a diagnostic result of the operation of the mentioned first integrated circuit element carried out by the mentioned second mutual diagnostic means, and the output of the mentioned abnormality detection means.
As a result, in the on-vehicle engine control apparatus of the invention, one single microprocessor can integrally control the first control output and the second control output closely related to the engine speed control. This facilitates transmitting and receiving mutually related control signals thereby response and performance in control being improved.
Furthermore, in the on-vehicle engine control apparatus of the invention, the load relay is operated on the basis of a diagnostic result of the first mutual diagnostic means and the second mutual diagnostic means cooperating each other in detecting an abnormality and an abnormality detection output of the abnormality detection means that monitors an abnormality in the operation of the sensor system, the control system, and the actuator system related to the throttle valve control. As a result, safety performance is improved and one single CPU can carry out integrally the engine drive control and the throttle control.
Another on-vehicle engine control apparatus according to the invention includes: a motor for carrying out an intake throttle valve opening control conforming to an output of one of a pair of accelerator position sensors that detects a degree of working an accelerator pedal and an output of one of a pair of throttle position sensors that detects the mentioned throttle valve opening; a load relay that controls an electric power supply to the mentioned motor; and a default position return mechanism that returns the mentioned throttle valve opening to a limp driving default position when the mentioned load relay interrupts the electric power supply. The control apparatus is supplied with a power from an on-vehicle battery via a power supply switch and generates at least a first control output that carries out drive control of the mentioned motor, a second control output that controls a solenoid valve for injecting a fuel to an engine, and a third output that drives the mentioned load relay. The on-vehicle engine control apparatus further includes: minimum threshold value setting means for setting a minimum threshold value that operates when a normal throttle position sensor output is not received and sets a predetermined engine speed slightly higher than an idle engine speed that is a minimum engine speed necessary for maintaining stable rotation of the engine; and normal threshold value means for setting a normal threshold value that operates when a normal throttle position sensor output is received and calculates and sets an engine speed which is approximately in inverse proportion to the throttle valve opening detected by the throttle position sensor.
The mentioned on-vehicle engine control apparatus further includes engine speed suppressing means for suppressing an engine speed. This engine speed suppressing means operates when the mentioned load relay is interrupted, and suppresses an engine speed by adjusting a fuel supply amount on the basis of the mentioned second control output, in response to a deviation between a predetermined engine speed set by the mentioned minimum threshold value setting means or by the normal threshold value setting means and an actual engine speed.
As a result, in the on-vehicle engine control apparatus of the invention, safety is improved by returning the throttle valve opening to the predetermined position using a fail-safe mechanism independent of electronic control. Even when the throttle valve opening is not returned to the normal position due to any abnormality in the fail-safe mechanism and none of the throttle position sensors are operating normally, it is possible to carry out limp driving at the minimum threshold engine speed.
In the on-vehicle engine control apparatus of the invention, even when the throttle valve opening is not returned to the normal position due to any abnormality in the fail-safe mechanism, it is possible to carry out limp driving at the normal threshold engine speed as long as the throttle position sensors are effective.
Furthermore, the foregoing normal threshold engine speed makes it possible to obtain an approximately constant engine output torque irrespective of a degree of the throttle valve opening that is stopped due to any abnormality.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.